The present invention relates to a fuel supply system for internal combustion engine using an ultrasonic atomizer for mixing of fuel and air, applied to a spark ignition type engine, distributing the fuel-air mixture generated by a fuel injection valve to multiple cylinders or to an engine using the fuel difficult to ignite at low temperature such as alcohol, kerosene, etc., and fuel and air are mixed by an ultrasonic atomizer to atomize liquid fuel.
Conventionally, a system to supply fuel-air mixture to engine is known, in which an ultrasonic atomizer is provided on the inlet pipe of internal combustion engine and fuel is atomized and mixed with intake air. For example, in the Japanese Provisional Pat. Publication No. 53-140416, it is proposed to provide a fuel supply system and an annular ultrasonic oscillator in the inlet pipe passage and to promote the mixing of atomized fuel obtained through annular ultrasonic oscillator with the intake air.
In the above conventional system, however, fuel supply system and ultrasonic oscillator are furnished closely to the engine in the inlet pipe passage. Accordingly, air flow is not stable and the intake air and the atomized fuel do not mix well, and fuel is often attached on pipe wall. Particularly, when fuel is attached on pipe wall in a high-powered engine, the transfer speed of fuel-air mixture is decreased at engine starting in low external air temperature and at the pickup time to rapidly accelerate from low speed, and the desired power cannot be obtained.
Also, because annular ultrasonic oscillator is used, fuel is not atomized at the nodal portion of vibration. Thus, the stagnated fuel drips and fuel supply becomes unstable.
On the other hand, an ultrasonic atomizer as shown in FIG. 16 is known as an atomizer to atomize liquid fuel. This consists of a cylinder 101, a nozzle body 102, an oscillator horn 103, and an electro-acoustic transducer 104. A fuel supply passage 105 is formed on the cylinder 101, and an injection hole 106 communicated with the fuel supply passage 105 is formed on the nozzle body 102. A plurality of injection holes 106 are furnished on the circumference of the nozzle body 102 and the fuel injected from the injection holes 106 is supplied to the oscillator horn 103 and is atomized.
However, in the above conventional type ultrasonic atomizer, the atomizing quantity is determined by the quantity of fuel supplied from the injection holes 106. Accordingly, the turndown ratio showing the ratio of maximum atomizing quantity and minimum atomizing quantity cannot be increased. Also, because it is difficult to evenly distribute the fuel into a plurality of injection holes 106 when it is placed to lateral direction, fuel is unevenly atomized. Further, the number of injection holes 106 must be increased in order to distribute the fuel evenly, but such increase is limited. Also, the manufacturing cost may be increased because the injection holes 106 are difficult to fabricate. Because the oscillator horn 103 is designed in horn shape with outer diameter increasing toward the tip, the atomizing angle of the atomized fuel becomes larger when it is installed on engine, and the atomized fuel is attached on inner wall of inlet pipe.